JP2014506017A - Strain balance laser diode - Google Patents

Abstract

According to the concept of the present disclosure, the use of Al in the waveguide layer of the laser is an InGaN / Al () comprising an optical confinement well (22; InGaN) and a strain compensation barrier (24; Al (In) GaN). A laser diode waveguide configuration represented in the form of an In) GaN waveguide superstructure (20) is contemplated. The composition of the optical confinement well (22) is selected so as to achieve strong optical confinement and not absorb the excitation emission even in the presence of the Al (In) GaN strain compensation barrier (24). The composition of the strain compensation barrier (24) is selected such that the tensile strain exhibited by Al (In) GaN compensates for the compressive strain of the InGaN optical confinement well (22), but does not interfere with optical confinement.

Description

Explanation of related applications

  This application claims the benefit of priority of US Patent Application No. 13 / 029,723, filed February 17, 2011, the contents of which are incorporated herein by reference, under 35 USC This is what we insist on.

  The present disclosure relates to semiconductor lasers, and more particularly to an optical waveguide structure that suppresses the formation of misfit defects and achieves relatively high optical confinement in the active region of the waveguide structure. The semiconductor laser according to the present disclosure is particularly well suited for, for example, an electrically pumped green laser diode.

  The inventors have found that the electrically excited green based on III-nitride compounds because of the potentially higher optical gain and higher uniformity, especially when the active region is made from InGaN quantum wells It has been recognized that it would be advantageous to use a semipolar substrate for laser diode design and manufacture. The present inventors have also recognized that the formation of misfit defects is a particularly serious problem for laser diode structures grown on semipolar substrates, since during the growth of AlGaN or InGaN layers. This is because a strong tensile strain and a compressive strain are accumulated, and misfit dislocations are formed when the strain is relaxed. Due to this misfit dislocation, the efficiency and reliability of light emission can be insufficient.

  The inventors have recognized that the presence of Al in the waveguide layer of a laser diode is generally considered undesirable, which is that AlGaN and AlInGaN do not contain Al. This is because the refractive index is considered to be lower than that of similar materials such as GaN and InGaN. For this reason, it is a general tendency that Al is not as close to the waveguide core as possible. Nonetheless, the inventors have found that Al and InGaN in the waveguide layer of a semiconductor laser diode because the Al-containing layer does not interfere with the high refractive index provided by the InGaN layer while achieving strain compensation for the InGaN layer. Recognized that using can be advantageous. This enhances optical confinement and optical gain while maintaining high crystal quality of the structure.

  According to the concepts of the present disclosure, the use of Al in the laser waveguide layer comprises one or more optical confinement wells (InGaN) and one or more corresponding strain compensation barriers (Al (In) GaN). A laser diode waveguide configuration, represented in the form of an InGaN / Al (In) GaN waveguide superstructure, is contemplated. The composition of the optical confinement well is selected so as to achieve strong optical confinement and not absorb excitation emission even in the presence of an Al (In) GaN strain compensation barrier. The composition of the strain compensation barrier is selected such that the tensile strain exhibited by Al (In) GaN compensates for the compressive strain of the InGaN optical confinement well, but does not interfere with optical confinement.

According to an embodiment of the present disclosure, a laser diode is provided that includes a semipolar GaN substrate, an active region, a waveguide region, and upper and lower cladding regions. The waveguide region includes at least one waveguide superstructure, which includes one or more In _y Ga _1-y N optical confinement wells with a well thickness a and a barrier layer that defines a strain compensation structure. And one or more intervening Al _x In _z Ga _1-xz N strain compensation barriers of thickness b, where x, y, and z are approximately 0.02 ≦ x ≦ 0.40, 0.05 ≦ y ≦ 0.35 and 0 ≦ z ≦ 0.10. The intervening strain compensation barrier contains sufficient Al to compensate for the strain introduced by the optical confinement well. When multiple optical confinement wells are employed, the In concentration and thickness within the wells need not be the same for each well. Similarly, when multiple barrier layers are employed, the barrier In and Al concentrations and thickness need not be the same for each barrier layer.

  According to another embodiment of the present disclosure, x, y, and z are approximately 0.02 ≦ x ≦ 0.40, 0.15 ≦ y ≦ 0.35, and 0 <z ≦ 0.10. The related and intervening strain compensation barrier contains enough Al to compensate for most of the strain introduced by the optical confinement well.

  According to yet another embodiment of the present disclosure, the optical confinement well includes a quantum well and the strain compensation barrier includes a quantum well barrier layer.

  The following detailed description of certain embodiments of the present disclosure is best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

Schematic diagram schematically illustrating a laser diode structure including a waveguide region according to an embodiment of the present disclosure. Graph showing the relationship between the concentration of Al and In, respectively, in the barrier and well of the waveguide region according to certain embodiments of the present disclosure

  A laser diode 100 shown in FIG. 1 is typically a laser diode according to an embodiment of the present disclosure, and includes a semipolar GaN substrate 10 and an active region 15, which are above (p side) and below (n side). ) A waveguide region with waveguide superstructure 20, upper and lower cladding regions 30, and upper and lower contact layers 40. The semipolar GaN substrate 10 is cut along the semipolar crystal growth surface, and the growth surface has a potentially high optical gain and the uniformity of the indium composition in the InGaN quantum well grown on the substrate. The inventors have recognized that this is advantageous because it improves. The inventors have also recognized the inherent challenges of using a semipolar growth surface in a laser diode structure. Specifically, many laser diode structures on a semipolar growth surface are very sensitive to the formation of crystal lattice misfit defects. The present disclosure addresses this design problem by utilizing a waveguide region having one or more strain-balanced waveguide superstructures 20 in a laser diode structure. The concept of the present invention can be implemented without including the upper (p-side) waveguide superstructure 20 and, in many cases, typically a strain balance superstructure need not be used on the active region 15. The strain balanced optical waveguide superstructure described herein is intended to be employed only within the lower waveguide superstructure 20.

  FIG. 1 shows a schematic diagram of the overall structure of a particular laser diode 100 incorporating a waveguide superstructure according to the present disclosure. Various alternative laser configurations are possible that incorporate the waveguide superstructure of the present disclosure. For example, the present disclosure contemplates using various alternative configurations for the active region 15, the cladding region 30, and the contact layer 40. It is believed that the cladding layer 30 of the laser diode structure may include GaN, AlGaN, AlInGaN, or some combination thereof, and the material composition of the two cladding layers may be different, It is contemplated that it may vary across the cladding layer. Similarly, the active region 15 can take a variety of forms, including, for example, an active multiple quantum well (MQW).

  Furthermore, it should be noted that laser configurations according to the present disclosure typically incorporate additional layers not shown in FIG. 1, such as buffer layers, electron / hole blocking layers, and the like. In each active region, waveguide region, and further upper and lower cladding regions, the upper and lower waveguide superstructures 20 in the waveguide region lead to stimulated emission of photons from the active region 15, and the cladding region 30 further includes the waveguide region. A multi-layer laser diode 100 is formed on the semipolar crystal growth surface of the semipolar GaN substrate 10 to promote the propagation of the emitted photons in the superstructure 20.

Regardless of its inherent configuration, the active region 15 is configured to stimulate and emit electrically or optically excited photons at the oscillation wavelength λ _C. The waveguide superstructure 20 is designed to define an absorption edge wavelength λ _W that is smaller than the oscillation wavelength λ _C and preferably approximately 10 nm ≦ (λ _C −λ _W ) ≦ 60 nm. In some embodiments, for example, if the target distortion compensation is substantially less than 100%, this wavelength separation may exceed 60 nm. In another embodiment, the appropriate wavelength separation range is narrower, and the absorption edge wavelength λ _W is approximately 10 nm ≦ (λ _C −λ _W ) ≦ 20 nm. In any case, the band gap of the waveguide superstructure 20 is relatively close to the excitation photon energy, but the waveguide superstructure 20 does not absorb oscillation light.

The waveguide superstructure 20 may be periodic or aperiodic, ie, the thickness of the optical confinement well 22 and the strain compensation barrier may be constant across the superstructure 20, or It is intended to change. It is also contemplated that the waveguide superstructure may be configured as a passive MQW waveguide layer. In this case, the optical confinement well 22 includes a nanometer-scale quantum well, and the strain compensation barrier 24 includes a quantum well barrier layer. In one example, when the waveguide superstructure 20 is configured as a passive MQW waveguide layer, a green laser diode with an emission wavelength of 530 nm ensures that the absorption edge of the passive QW is sufficiently close to the oscillation wavelength, ie, the difference is about 20 The passive MQW waveguide layer is configured to have an emission wavelength of about 510 nm so that it is ˜60 nm. In many embodiments, it may be preferable to ensure that this wavelength difference is 10 nm or more to prevent suppression of optical gain by the passive MQW waveguide layer. When the oscillation wavelength λ _C is between approximately 500 nm and approximately 540 nm, it is considered that the absorption edge wavelength λ _W may be between approximately 430 nm and approximately 530 nm.

A waveguide superstructure 20 according to the present disclosure includes a plurality of In _y Ga _{1 -y} N optical confinement wells 22 and an intervening Al _x In _z Ga _{1 -xz} N strain compensation barrier 24 defining a strain compensation structure. In the formula, x and z are approximately in a relationship of 0.02 ≦ x ≦ 0.40 and 0 ≦ z ≦ 0.10. In general cases, the value of y is approximately 0.05 ≦ y ≦ 0.35, but for a structure in which strain compensation is close to 100%, that is, the Al concentration x in the strain compensation barrier is relatively low. When it is high, in order to maintain a sufficiently high average refractive index, it is preferable that the relationship is approximately 0.15 ≦ y ≦ 0.35. In certain embodiments, x is approximately 0.05 ≦ x ≦ 0.20 and z is approximately 0 <z ≦ 0.10. It is also contemplated that the In molar concentration may not be constant within one or more optical confinement wells. In this case, for each optical confinement well, y refers to the average In molar concentration in the optical confinement well. It is further contemplated that the In molar concentration and Al molar concentration may not be constant within one or more strain compensation barriers. In this case, for each strain compensation barrier, x refers to the average Al molar concentration within the strain compensation barrier and z refers to the average In molar concentration within the strain compensation barrier. Furthermore, it is also contemplated that in the waveguide superstructure, the In molar concentration y of the optical confinement well may be different, and at the same time the Al molar concentration x and In molar concentration y of the strain compensation barrier may be different. .

  The present inventors have recognized that unlike InGaN, the refractive index of Al (In) GaN decreases approximately linearly with the Al concentration. This is because the absorption edge of Al (In) GaN in the composition range is far from the excitation photon energy. At the same time, the refractive index of InGaN in the specified range increases superlinearly with the In concentration because InGaN has a lower bandgap that is closer to the excitation photon energy. Furthermore, the tensile strain in Al (In) GaN increases linearly with Al concentration, while the compressive strain of InGaN wells increases linearly with In content as well. Thus, the intervening Al (In) GaN strain compensation barrier 24 can be easily designed to contain enough Al to compensate for the strain induced by the optical confinement well 22, ie, the formation of misfit dislocations. However, due to the optical confinement well, the average refractive index does not decrease strongly and remains higher than that of GaN. If the In concentration in the Al (In) GaN strain compensation barrier 24 is not zero, the combination of Al and In concentrations should be selected to provide tensile strain.

For example, in green laser emission, that is, 530 nm, the decrease in Al (In) GaN refractive index with Al concentration is small. Therefore, the Al (In) GaN strain compensation barrier 24 realizes strain compensation, but does not strongly decrease the average refractive index of the waveguide core formed by the active region 15 and the waveguide superstructure 20. Since the GaN / Al (In) GaN structure was typically expected to have a lower refractive index than n-type GaN, the present inventors have found that this approach is counterintuitive. In fact, the refractive index of tensile strained Al _x In _z Ga _1-xz N is lower than that of the GaN substrate 10 and the upper and lower cladding layers 30, but when the absorption edge of the InGaN optical confinement well is sufficiently close to the oscillation wavelength, The inventors have recognized that the average refractive index of the waveguide superstructure 20 is significantly higher than that of the GaN substrate 10 and the upper and lower cladding layers 30.

  It should be noted that in some embodiments of the present disclosure, the primary relaxation mechanism helps relaxation along the c-axis. However, the AlN / GaN lattice mismatch at the c-axis is 3.9%, which is higher than that at the a-axis or m-axis (2.4%). Accordingly, distortion compensation in the c direction is effective for the embodiments of the present disclosure. As a result, using a waveguide superstructure incorporating an Al (In) GaN strain compensation barrier according to the present disclosure provides a large total refractive index contrast and at least partially or fully compensates for compressive strain in the projected c-direction. The waveguide region can be grown. For example, a 17 nm AlGaN barrier layer with an Al concentration of approximately 10% may be used to fully compensate for strain in the c-axis direction of an InGaN optical confinement well with a thickness of 2.5 nm and an In concentration of 25%. . Alternatively, if the Al concentration in the barrier layer is lower, a thicker one will be required.

  In many embodiments, it will not be difficult to ensure that the thickness of the waveguide superstructure according to the present disclosure exceeds approximately 70 nm. In many embodiments, a suitable well thickness a is between about 2 nm and about 5 nm and should not exceed about 60 nm. The thickness of the barrier layer is limited by the desired thickness of the waveguide core, since excessive core thickness can lead to reduced optical confinement. The typical thickness of the waveguide core is approximately 70-300 nm above and below the active region of the core. Thus, in some embodiments of the present disclosure, the total thickness of all strain compensation barriers in the waveguide superstructure should not exceed 300 nm.

  In one embodiment of the present disclosure, the rate of distortion compensation can be characterized by the ratio θ, where θ> 0 and θ = 1 represents complete distortion compensation, which is typically preferred. The thicknesses a and b of the optical confinement well 22 and the intervening strain compensation barrier 24 satisfy the following relationship.

(0.1y) η≈θ (0.039x + 0.1z) (1−η)
Where y is averaged over the all-optical confinement well, x and z are averaged over the total strain compensation barrier, and η is In _y Ga ₁ in the waveguide superstructure 20. _-y N duty cycle of the confinement well and a / b = η / (1-η). The Al _x In _z Ga _{1 -xz} N strain compensation barrier can be easily configured to provide sufficient tensile strain to compensate for most of the compressive strain provided by the In _y Ga _{1 -y} N optical confinement well. It is believed that. FIG. 2 illustrates the relationship between Al and In concentrations for various InGaN duty cycles in a waveguide region according to certain embodiments of the present disclosure. A suitable duty cycle is considered to range from approximately 5% to approximately 50%. In the case of an aperiodic structure, the strain compensation coefficient θ can be calculated using the total thicknesses a and b of the optical confinement well 22 and the intervening strain compensation barrier 24.

  In order to increase the refractive index of InGaN extremely linearly with the In concentration y, it is preferable to use a sufficiently high In concentration in the InGaN optical confinement well. In order to obtain a waveguide superstructure having a desired strain compensation coefficient θ and an average refractive index significantly higher than the refractive index of the GaN substrate, the In concentration y in the optical confinement well is approximately 0.15θ ≦ y ≦ 0. 35 is considered preferable. By doing so, the concept of the present disclosure is implemented in this way, while using the Al concentration x necessary to obtain the desired distortion compensation coefficient θ, while keeping the absorption edge of the optical confinement well sufficiently close to the oscillation wavelength. Thus, it is convenient to obtain a sufficiently high average refractive index.

  In the embodiment shown in FIG. 1, the waveguide region of the laser diode 100 includes at least one waveguide superstructure 20 on each side of the active region 15. However, the laser diode structure according to the present disclosure may simply comprise the waveguide superstructure 20 only on the n-side of the laser diode structure, while the p-side waveguide may be a conventional InGaN or GaN waveguide layer, or an alternative It is believed that future waveguide layers may be included. Preferably, the p-side waveguide layer is further adjusted so that its thickness and In concentration are small enough to prevent relaxation. In other words, the waveguide core composed of the active region and the waveguide layer may be asymmetric and shift the optical mode to the n side. The advantage of this asymmetric configuration is that there is less mode transmission through the p-type material and light loss is reduced.

  Considering embodiments in which the waveguide region of the laser diode 100 includes at least one waveguide superstructure 20 on each side of the active region 15, the waveguide region is typically p-doped disposed on both sides of the active region 15. The waveguide superstructure and the n-doped waveguide superstructure 20, and the cladding region typically includes a p-doped layer and an n-doped layer 30 disposed on either side of the active region 15. In this case, it can be said that the active region 15 is disposed between the p-doped side and the n-doped side of the laser diode 100. The strain compensation barrier 24 interposed between the optical confinement wells 22 on the n-doped side of the laser diode is n-doped, and the strain compensation barrier 24 interposed between the optical confinement wells 22 on the p-doped side of the laser diode is p-doped. The foregoing conditions for the layers on the n-doped side and the p-doped side of the laser diode mainly relate to the embodiment in which the waveguide superstructure is provided on each side of the active region, and many embodiments of the present disclosure Note that no strain-balanced waveguide superstructure is required on either side of the active region.

It is contemplated that a laser diode according to the present disclosure may comprise one or more additional optical confinement layers in the form of a bulk InGaN layer or InGaN / GaN superlattice configured to improve optical confinement at the oscillation wavelength λ _C. ing. The waveguide superstructure 20 may be sandwiched between the active region 15 and an additional confinement layer such as a bulk InGaN layer or an InGaN / GaN superlattice. The thickness of each of the bulk InGaN layer or InGaN / GaN superlattice should be thin enough to prevent strain-induced relaxation in the laser diode. As described above, it may be more preferable that the laser diode 100 is provided with an electron blocking layer on the active region 15. The electron blocking layer may be placed in the active region or between the active region and a waveguide layer that may include a waveguide superstructure. For example, but not limited to, the electronic blocking layer may be constructed in accordance with the teachings of US Patent Application Publication No. 2010/0150193 (A1). The laser diode 100 may include a hole blocking layer between the active region 15 and the n-side waveguide layer that may include the waveguide superstructure 20. These electron blocking and hole blocking layers will preferably comprise AlGaN or AlInGaN having a wider band gap than the barrier band gap between the quantum wells in the active region. Since the electron block layer and hole block layer will contain Al, they will also contribute to distortion compensation. It may be preferable to place an electron blocking layer between the active region and all p-side InGaN layers, while simultaneously placing a hole blocking layer between the active region and all n-side InGaN layers.

  For purposes of illustration and not limitation, several embodiments according to the concepts of the present disclosure are already contemplated.

Laser diode structure with the following layers (from bottom to top)
-N-GaN buffer layer and cladding layer-Passive multiple quantum well with 8-12 periods, wherein 2-5 nm passive QW is separated by 10 nm AlInGaN or AlGaN barrier (AlGaN has an Al concentration of 5 The passive quantum well is configured such that its emission wavelength is 10 to 40 nm shorter than the oscillation wavelength.

Two or three periods of InGaN active quantum wells configured to provide optical gain in the green spectral region (500-540 nm), an AlInGaN electron blocking layer, and
A p-side GaN cladding layer having a thickness of 600 to 1200 nm

  Similar to Example 1 except that an AlInGaN cladding layer is used at least in the n-side cladding layer. The AlInGaN layer lattice coincides in one in-plane direction (typically in the direction towards the c-axis), and the strain in the other direction of the AlInGaN layer lattice is sufficiently low to avoid relaxation. The p-side cladding layer may include an AlInGaN or AlGaN layer. Each cladding layer may be made from a combination of an AlGaN layer, a GaN layer, an InGaN layer, or an AlInGaN layer. This structure may further include a bulk InGaN layer or InGaN / GaN superlattice in the waveguide core in addition to the strain compensated passive QW to further improve optical confinement. In the presence of a strain compensated passive QW, optical confinement is enhanced so that it is no longer necessary to increase the In concentration of the bulk layer or superlattice or increase the thickness of the bulk layer or superlattice. These can be made so thin that relaxation can be avoided. Also, because of the high refractive index of passive quantum wells, in some designs it is preferable to position the passive quantum well between the active region and this additional layer.

  Laser diode structure comprising two passive wells, including a 5 nm n-AlInGaN barrier below them and a 17 nm n-AlInGaN barrier above them. The two passive QWs are separated by a 17 nm thick AlInGaN barrier layer. This structure is placed between the hole blocking layer and an n-InGaN / GaN superlattice with an average In concentration of 3% to 6%. The thickness of this n-superlattice is 114 nm, which is below the relaxation limit for (20-21) substrate orientation. An n-AlInGaN cladding layer or a combination of AlInGaN / GaN layers is placed under the n-InGaN / GaN superlattice layer. The structure further includes a 90 nm thick p-InGaN / GaN superlattice. A p-type GaN, AlGaN, AlInGaN, or combination cladding layer may be grown as in Examples 1 and 2. This structure should further comprise an electron blocking layer between the active region and the cladding layer.

  Laser diode structure similar to previous examples, except that there are more than two passive quantum wells. In this case, the passive quantum well is separated by an AlInGaN barrier. As passive QW provides more optical confinement, the n-type InGaN superlattice layer may be thinner.

  Laser diode structure with one passive QW. This design is similar to Example 3 except that there is only one passive quantum well and the InGaN superlattice is slightly thicker (120 nm).

  In this document, a statement that “configured” so that the components of the present disclosure embody a specific property or function in a specific manner is not a description of the intended use, but a structural description. Please keep in mind. More specifically, when a component is referred to in this document as being “configured”, this is an indication of the existing physical condition of the component, and thus the structural characteristics of the component. It should be understood as a clear description.

  When terms such as "preferred", "normal", and "typical" are used in this document, these terms are not intended to be used to limit the scope of the claimed invention or are It should be noted that these features are not used to imply that they are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely to identify particular aspects of the embodiments of the present disclosure or to highlight alternative or additional features that may or may not be utilized in certain embodiments of the present disclosure. is there.

  For purposes of describing and defining the present invention, the term “approximately” is used herein to describe the degree of inherent uncertainty that may result from any quantitative comparison, value, measurement, or other representation. Note that it is used. Furthermore, the term “substantially” is used herein to describe the degree to which a quantitative expression can vary from the stated criteria without causing a change in the basic function of the subject matter being discussed.

  Although the subject matter of the present disclosure has been described in detail and with reference to specific embodiments thereof, it is possible to make modifications and variations without departing from the scope of the invention as defined in the appended claims. It will be clear. More specifically, although some aspects of the present disclosure have been identified herein as being preferred or particularly advantageous, it is intended that the present disclosure is not necessarily limited to these aspects. For example, while the present invention has been described primarily with reference to waveguide superstructure 20, it is contemplated that waveguide superstructure 20 may be configured as a passive MQW waveguide layer. In this case, the optical confinement well 22 will include a nanometer-scale quantum well, and the strain compensation barrier 24 will include a quantum well barrier layer. Typically, quantum well layers in passive MWQ structures are thinner than 10 nm.

  Note that one or more of the following claims uses the term “wherein” as a transitional phrase. To define the present invention, this term is introduced in the claims as an open-ended transition phrase, used to introduce a description of a set of features of the structure, and is a more commonly used open-ended preamble. Note that this should be interpreted in the same way as the term “comprising”.

10 Semipolar GaN substrate 15 Active region 20 Waveguide superstructure 22 Optical confinement well 24 Strain compensation barrier 30 Clad region 40 Contact layer 100 Laser diode

Claims (11)

In a laser diode comprising a semipolar GaN substrate, an active region, a waveguide region, and further upper and lower cladding regions,
The semipolar GaN substrate is cut along a semipolar crystal growth surface,
The active region is configured to stimulate and emit electrically excited photons at an oscillation wavelength λ _C ;
The waveguide region comprises at least one waveguide superstructure;
The waveguide superstructure includes a plurality of In _y Ga _{1 -y} N optical confinement wells having a well thickness a and a plurality of intervening Al _x In _z Ga ₁ -xz having a barrier layer thickness b defining a strain compensation structure. An N strain compensation barrier, wherein x, y, and z are approximately 0.02 ≦ x ≦ 0.40, 0.05 ≦ y ≦ 0.35, and 0 ≦ z ≦ 0.10. Relationship
The intervening strain compensation barrier comprises sufficient Al to compensate for strain introduced by the optical confinement well;
Said In _y Ga _1-y N light confining wells giving a compressive strain, and the _{Al x In z Ga 1-xz} N distortion compensation barrier, the In _y Ga _1-y the compression provided by the N optical confinement wells Give enough tensile strain to compensate for most of the strain,
The active region and the waveguide, such that the waveguide region directs stimulated emission of the photons from the active region and the cladding region facilitates propagation of the emitted photons within the waveguide region. A region and each of the upper and lower cladding regions is formed as a multi-layer laser diode on the semipolar crystal growth surface of the semipolar GaN substrate;
Where (a) the waveguide superstructure is configured as a passive MQW waveguide layer, (b) the optical confinement well includes a quantum well, and (c) the strain compensation barrier includes a quantum well barrier layer, A laser diode characterized by being at least one of the above. The intervening strain compensation barrier includes sufficient Al to compensate the strain introduced by the optical confinement well to a strain compensation ratio θ, where θ> 0 and θ = 1 provides complete strain compensation. Represent,
The thicknesses a and b of the optical confinement well and the intervening strain compensation barrier are related,
(0.1y) η≈θ (0.039x + 0.1z) (1−η)
Where x, y, and z are averaged over the waveguide superstructure, and η is the duty cycle of the periodic or aperiodic In _y Ga _1-y N confinement well or the 2. The laser diode according to claim 1, wherein the laser diode has an average duty cycle in the waveguide superstructure and a / b = [eta] / (1- [eta]). The waveguide superstructure is characterized by an absorption edge wavelength λ _{W having} a relationship of approximately 10 nm ≦ (λ _C −λ _W ) ≦ 60 nm or a relationship of 10 nm ≦ (λ _C −λ _W ) ≦ 40 nm Is,
The average refractive index of the waveguide superstructure is higher than the GaN substrate and the upper and lower cladding regions, or
The waveguide superstructure includes a plurality of Al _x In _z Ga _1-xz N strain compensation barriers that _collectively define a thickness of less than about 300 nm;
The laser diode according to claim 1, wherein the laser diode is at least one of the following. The well thickness a is between about 2 nm and about 5 nm;
The well thickness a does not exceed about 60 nm,
For at least one strain compensation barrier, x is approximately 0.05 ≦ x ≦ 0.20, or
Z is approximately 0 <z ≦ 0.10 for at least one strain compensation barrier;
The laser diode according to claim 1, wherein the laser diode is at least one of the following. The intervening strain compensation barrier contains sufficient Al to compensate for substantially all strain introduced by the optical confinement well such that the strain compensation ratio θ is greater than 0.9 or greater than 0.5. ,And,
2. The laser diode according to claim 1, wherein y is approximately 0.15 ≦ y ≦ 0.35 with respect to at least one optical confinement well.   The waveguide region of the laser diode has at least one waveguide superstructure on each side of the active region in the multi-layer laser diode, and each waveguide superstructure guides the photons from the active region. 2. The laser diode according to claim 1, wherein the laser diode is included so as to guide emission. The oscillation wavelength λ _C is between approximately 500 nm and approximately 540 nm, the absorption edge wavelength λ _W is approximately between 430 nm and approximately 530 nm, and the absorption edge wavelength λ _W is approximately 10 nm ≦ (λ _C −λ _2. The laser diode according to claim 1, wherein a relationship of _W ) ≦ 20 nm is established. The laser diode further comprises one or more additional confinement layers in the form of a bulk InGaN layer or InGaN / GaN superlattice configured to improve optical confinement of the oscillation wavelength λ _C ;
The thickness of each of the bulk InGaN layer or InGaN / GaN superlattice is thin enough to prevent strain-induced relaxation in the laser diode;
The laser diode of claim 1, wherein the waveguide superstructure is sandwiched between the active region and the additional confinement layer.   The laser diode includes an asymmetric waveguide core comprising the active region and the waveguide superstructure configured to shift the optical mode of a laser to the n-side of the laser diode; The laser diode according to claim 1. In a laser diode comprising a semipolar GaN substrate, an active region, a waveguide region, and further upper and lower cladding regions, where
The semipolar GaN substrate is cut along a semipolar crystal growth surface,
The active region is configured to stimulate and emit electrically excited photons at an oscillation wavelength λ _C ;
The waveguide region comprises at least one waveguide superstructure;
The waveguide superstructure includes at least one In _y Ga _1-y N optical confinement well having a well thickness a and one or more intervening Al _x In _z Ga ₁ having a barrier layer thickness b defining a strain compensation structure. _-xz N strain compensation barrier, where x, y, and z are approximately 0.02 ≦ x ≦ 0.40, 0.05 ≦ y ≦ 0.35, and 0 ≦ z ≦ 0.10. Relationship,
The intervening strain compensation barrier contains sufficient Al to compensate most of the strain introduced by the optical confinement well to a strain compensation ratio θ, where θ> 0 and θ = 1 is perfect Represents distortion compensation,
The thicknesses a and b of the optical confinement well and the intervening strain compensation barrier are related,
(0.1y) η≈θ (0.039x + 0.1z) (1−η)
Where x, y, and z are averaged over the waveguide superstructure, and η is the duty cycle of the periodic or aperiodic In _y Ga _1-y N confinement well or the The average duty cycle in the waveguide superstructure, and a / b = η / (1-η),
The active region and the waveguide, such that the waveguide region directs stimulated emission of the photons from the active region and the cladding region facilitates propagation of the emitted photons within the waveguide region. Each of the region and the upper and lower cladding regions is formed as a multi-layer laser diode on the semipolar crystal growth surface of the semipolar GaN substrate. In a laser diode comprising a semipolar GaN substrate, an active region, a waveguide region, and further upper and lower cladding regions, where
The semipolar GaN substrate is cut along a semipolar crystal growth surface,
The active region is configured to stimulate and emit electrically excited photons at an oscillation wavelength λ _C ;
The waveguide region includes at least one waveguide superstructure, and the waveguide region is characterized by an absorption edge wavelength λ _{W having} a relationship of approximately 10 nm ≦ (λ _C −λ _W ) ≦ 20 nm. Yes,
The waveguide superstructure is configured as a passive MQW waveguide layer, and the waveguide superstructure defines a strain compensation structure and a plurality of In _y Ga _1-y N optical confinement wells having a well thickness a. And an Al _x In _z Ga _1-xz N strain compensation barrier with a layer thickness b interposed therebetween, where x, y, and z are approximately 0.02 ≦ x ≦ 0.40 and 0.15 ≦ y ≦. 0.35 and 0 <z ≦ 0.10,
The optical confinement well comprises a quantum well;
The strain compensation barrier comprises a quantum well barrier layer;
The intervening strain compensation barrier contains sufficient Al to compensate most of the strain introduced by the optical confinement well to a strain compensation ratio θ, where θ> 0 and θ = 1 is perfect Represents distortion compensation,
The thicknesses a and b of the optical confinement well and the intervening strain compensation barrier are related,
(0.1y) η≈θ (0.039x + 0.1z) (1−η)
Where x, y, and z are averaged over the waveguide superstructure, and η is the duty cycle of the In _y Ga _1-y N confinement well in the waveguide superstructure And a / b = η / (1-η),
The refractive index of the Al _x In _z Ga _1-xz N with tensile strain is lower than the GaN substrate and the upper and lower cladding regions;
An average refractive index of the waveguide superstructure is higher than the GaN substrate and the upper and lower cladding regions;
The active region and the waveguide, such that the waveguide region directs stimulated emission of the photons from the active region and the cladding region facilitates propagation of the emitted photons within the waveguide region. Each of the region and the upper and lower cladding regions is formed as a multi-layer laser diode on the semipolar crystal growth surface of the semipolar GaN substrate.

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